/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package com.googlecode.httl.support.util;

import java.util.Comparator;

/**
 * ClassComparator. (Tool, Singleton, ThreadSafe)
 * 
 * @author Liang Fei (liangfei0201 AT gmail DOT com)
 */
public class ClassComparator implements Comparator<Class<?>> {

    public static final ClassComparator COMPARATOR = new ClassComparator();

    private ClassComparator() {
    }

    public int compare(Class<?> o1, Class<?> o2) {
        if (o1 == null && o2 == null) {
            return 0;
        }
        // 空值排在后面
        if (o1 == null) {
            return 1;
        }
        if (o2 == null) {
            return -1;
        }
        // 父类型排在后面
        if (o1.isAssignableFrom(o2)) { // o1是o2的父类型
            return 1;
        }
        if (o2.isAssignableFrom(o1)) { // o2是o1的父类型
            return -1;
        }
        // 互不相关的类型按类名排序
        return o1.getName().compareTo(o2.getName());
    }
}

